[PATCH 3/6] x86: relocs: add 64-bit ELF support to relocs tool
From: Kees Cook
Date: Fri Apr 12 2013 - 16:14:40 EST
This adds the ability to process relocations from the 64-bit kernel ELF,
if built with ELF_BITS=64 defined. The special case for the percpu area is
handled, along with some other symbols specific to the 64-bit kernel.
Based on work by Neill Clift and Michael Davidson.
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
arch/x86/tools/relocs.c | 267 +++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 261 insertions(+), 6 deletions(-)
diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index bdc5930..1f7ff3d 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -17,19 +17,39 @@
#define _ElfW(bits, type) __ElfW(bits, type)
#define __ElfW(bits, type) Elf##bits##_##type
+#ifndef ELF_BITS
#define ELF_BITS 32
+#endif
+
+#if (ELF_BITS == 64)
+#define ELF_MACHINE EM_X86_64
+#define ELF_MACHINE_NAME "x86_64"
+#define SHT_REL_TYPE SHT_RELA
+#define Elf_Rel Elf64_Rela
+#else
#define ELF_MACHINE EM_386
#define ELF_MACHINE_NAME "i386"
#define SHT_REL_TYPE SHT_REL
+#define Elf_Rel ElfW(Rel)
+#endif
+#if (ELF_BITS == 64)
+#define ELF_CLASS ELFCLASS64
+#define ELF_R_SYM(val) ELF64_R_SYM(val)
+#define ELF_R_TYPE(val) ELF64_R_TYPE(val)
+#define ELF_ST_TYPE(o) ELF64_ST_TYPE(o)
+#define ELF_ST_BIND(o) ELF64_ST_BIND(o)
+#define ELF_ST_VISIBILITY(o) ELF64_ST_VISIBILITY(o)
+#else
#define ELF_CLASS ELFCLASS32
#define ELF_R_SYM(val) ELF32_R_SYM(val)
#define ELF_R_TYPE(val) ELF32_R_TYPE(val)
#define ELF_ST_TYPE(o) ELF32_ST_TYPE(o)
#define ELF_ST_BIND(o) ELF32_ST_BIND(o)
#define ELF_ST_VISIBILITY(o) ELF32_ST_VISIBILITY(o)
+#endif
-#define Elf_Rel ElfW(Rel)
+#define Elf_Addr ElfW(Addr)
#define Elf_Ehdr ElfW(Ehdr)
#define Elf_Phdr ElfW(Phdr)
#define Elf_Shdr ElfW(Shdr)
@@ -48,6 +68,7 @@ struct relocs {
static struct relocs relocs16;
static struct relocs relocs32;
+static struct relocs relocs64;
struct section {
Elf_Shdr shdr;
@@ -77,6 +98,9 @@ static const char * const sym_regex_kernel[S_NSYMTYPES] = {
"^(xen_irq_disable_direct_reloc$|"
"xen_save_fl_direct_reloc$|"
"VDSO|"
+#if (ELF_BITS == 64)
+ "__vvar_page|"
+#endif
"__crc_)",
/*
@@ -100,6 +124,11 @@ static const char * const sym_regex_kernel[S_NSYMTYPES] = {
"__end_rodata|"
"__initramfs_start|"
"(jiffies|jiffies_64)|"
+#if (ELF_BITS == 64)
+ "__per_cpu_load|"
+ "init_per_cpu__.*|"
+ "__end_rodata_hpage_align|"
+#endif
"_end)$"
};
@@ -226,6 +255,24 @@ static const char *rel_type(unsigned type)
{
static const char *type_name[] = {
#define REL_TYPE(X) [X] = #X
+#if (ELF_BITS == 64)
+ REL_TYPE(R_X86_64_NONE),
+ REL_TYPE(R_X86_64_64),
+ REL_TYPE(R_X86_64_PC32),
+ REL_TYPE(R_X86_64_GOT32),
+ REL_TYPE(R_X86_64_PLT32),
+ REL_TYPE(R_X86_64_COPY),
+ REL_TYPE(R_X86_64_GLOB_DAT),
+ REL_TYPE(R_X86_64_JUMP_SLOT),
+ REL_TYPE(R_X86_64_RELATIVE),
+ REL_TYPE(R_X86_64_GOTPCREL),
+ REL_TYPE(R_X86_64_32),
+ REL_TYPE(R_X86_64_32S),
+ REL_TYPE(R_X86_64_16),
+ REL_TYPE(R_X86_64_PC16),
+ REL_TYPE(R_X86_64_8),
+ REL_TYPE(R_X86_64_PC8),
+#else
REL_TYPE(R_386_NONE),
REL_TYPE(R_386_32),
REL_TYPE(R_386_PC32),
@@ -241,6 +288,7 @@ static const char *rel_type(unsigned type)
REL_TYPE(R_386_PC8),
REL_TYPE(R_386_16),
REL_TYPE(R_386_PC16),
+#endif
#undef REL_TYPE
};
const char *name = "unknown type rel type name";
@@ -281,15 +329,42 @@ static const char *sym_name(const char *sym_strtab, Elf_Sym *sym)
return name;
}
+static Elf_Sym *sym_lookup(const char *symname)
+{
+ int i;
+ for (i = 0; i < ehdr.e_shnum; i++) {
+ struct section *sec = &secs[i];
+ long nsyms;
+ char *strtab;
+ Elf_Sym *symtab;
+ Elf_Sym *sym;
+ if (sec->shdr.sh_type != SHT_SYMTAB)
+ continue;
+
+ nsyms = sec->shdr.sh_size/sizeof(Elf_Sym);
+ symtab = sec->symtab;
+ strtab = sec->link->strtab;
+
+ for (sym = symtab; --nsyms >= 0; sym++) {
+ if (!sym->st_name)
+ continue;
+ if (strcmp(symname, strtab + sym->st_name) == 0)
+ return sym;
+ }
+ }
+ return 0;
+}
#if BYTE_ORDER == LITTLE_ENDIAN
#define le16_to_cpu(val) (val)
#define le32_to_cpu(val) (val)
+#define le64_to_cpu(val) (val)
#endif
#if BYTE_ORDER == BIG_ENDIAN
#define le16_to_cpu(val) bswap_16(val)
#define le32_to_cpu(val) bswap_32(val)
+#define le64_to_cpu(val) bswap_64(val)
#endif
static uint16_t elf16_to_cpu(uint16_t val)
@@ -304,9 +379,20 @@ static uint32_t elf32_to_cpu(uint32_t val)
#define elf_half_to_cpu(x) elf16_to_cpu(x)
#define elf_word_to_cpu(x) elf32_to_cpu(x)
+
+#if (ELF_BITS == 64)
+static uint64_t elf64_to_cpu(uint64_t val)
+{
+ return le64_to_cpu(val);
+}
+#define elf_addr_to_cpu(x) elf64_to_cpu(x)
+#define elf_off_to_cpu(x) elf64_to_cpu(x)
+#define elf_xword_to_cpu(x) elf64_to_cpu(x)
+#else
#define elf_addr_to_cpu(x) elf32_to_cpu(x)
#define elf_off_to_cpu(x) elf32_to_cpu(x)
#define elf_xword_to_cpu(x) elf32_to_cpu(x)
+#endif
static void read_ehdr(FILE *fp)
{
@@ -483,6 +569,9 @@ static void read_relocs(FILE *fp)
Elf_Rel *rel = &sec->reltab[j];
rel->r_offset = elf_addr_to_cpu(rel->r_offset);
rel->r_info = elf_xword_to_cpu(rel->r_info);
+#if (SHT_REL_TYPE == SHT_RELA)
+ rel->r_addend = elf_xword_to_cpu(rel->r_addend);
+#endif
}
}
}
@@ -491,6 +580,13 @@ static void read_relocs(FILE *fp)
static void print_absolute_symbols(void)
{
int i;
+ const char *format;
+
+ if (ehdr.e_ident[EI_CLASS] == ELFCLASS64)
+ format = "%5d %016"PRIx64" %5"PRId64" %10s %10s %12s %s\n";
+ else
+ format = "%5d %08"PRIx32" %5"PRId32" %10s %10s %12s %s\n";
+
printf("Absolute symbols\n");
printf(" Num: Value Size Type Bind Visibility Name\n");
for (i = 0; i < ehdr.e_shnum; i++) {
@@ -510,7 +606,7 @@ static void print_absolute_symbols(void)
if (sym->st_shndx != SHN_ABS) {
continue;
}
- printf("%5d %08x %5d %10s %10s %12s %s\n",
+ printf(format,
j, sym->st_value, sym->st_size,
sym_type(ELF_ST_TYPE(sym->st_info)),
sym_bind(ELF_ST_BIND(sym->st_info)),
@@ -524,6 +620,12 @@ static void print_absolute_symbols(void)
static void print_absolute_relocs(void)
{
int i, printed = 0;
+ const char *format;
+
+ if (ehdr.e_ident[EI_CLASS] == ELFCLASS64)
+ format = "%016"PRIx64" %016"PRIx64" %10s %016"PRIx64" %s\n";
+ else
+ format = "%08"PRIx32" %08"PRIx32" %10s %08"PRIx32" %s\n";
for (i = 0; i < ehdr.e_shnum; i++) {
struct section *sec = &secs[i];
@@ -576,7 +678,7 @@ static void print_absolute_relocs(void)
printed = 1;
}
- printf("%08x %08x %10s %08x %s\n",
+ printf(format,
rel->r_offset,
rel->r_info,
rel_type(ELF_R_TYPE(rel->r_info)),
@@ -636,8 +738,140 @@ static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel,
}
}
-static int do_reloc(struct section *sec, Elf_Rel *rel, Elf_Sym *sym,
- const char *symname)
+/*
+ * The .data..percpu section is a special case for x86_64 SMP kernels.
+ * It is used to initialize the actual per_cpu areas and to provide
+ * definitions for the per_cpu variables that correspond to their offsets
+ * within the percpu area. Since the values of all of the symbols need
+ * to be offsets from the start of the per_cpu area the virtual address
+ * (sh_addr) of .data..percpu is 0 in SMP kernels.
+ *
+ * This means that:
+ *
+ * Relocations that reference symbols in the per_cpu area do not
+ * need further relocation (since the value is an offset relative
+ * to the start of the per_cpu area that does not change).
+ *
+ * Relocations that apply to the per_cpu area need to have their
+ * offset adjusted by by the value of __per_cpu_load to make them
+ * point to the correct place in the loaded image (because the
+ * virtual address of .data..percpu is 0).
+ *
+ * For non SMP kernels .data..percpu is linked as part of the normal
+ * kernel data and does not require special treatment.
+ *
+ */
+static int per_cpu_shndx = -1;
+Elf_Addr per_cpu_load_addr;
+
+static void percpu_init(void)
+{
+ int i;
+ for (i = 0; i < ehdr.e_shnum; i++) {
+ ElfW(Sym) *sym;
+ if (strcmp(sec_name(i), ".data..percpu"))
+ continue;
+
+ if (secs[i].shdr.sh_addr != 0) /* non SMP kernel */
+ return;
+
+ sym = sym_lookup("__per_cpu_load");
+ if (!sym)
+ die("can't find __per_cpu_load\n");
+
+ per_cpu_shndx = i;
+ per_cpu_load_addr = sym->st_value;
+ return;
+ }
+}
+
+/*
+ * Check to see if a symbol lies in the .data..percpu section.
+ * For some as yet not understood reason the "__init_begin"
+ * symbol which immediately preceeds the .data..percpu section
+ * also shows up as it it were part of it so we do an explict
+ * check for that symbol name and ignore it.
+ */
+static int is_percpu_sym(ElfW(Sym) *sym, const char *symname)
+{
+ return (sym->st_shndx == per_cpu_shndx) &&
+ strcmp(symname, "__init_begin");
+}
+
+static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
+ const char *symname)
+{
+ unsigned r_type = ELF64_R_TYPE(rel->r_info);
+ ElfW(Addr) offset = rel->r_offset;
+ int shn_abs = (sym->st_shndx == SHN_ABS) && !is_reloc(S_REL, symname);
+
+ if (sym->st_shndx == SHN_UNDEF)
+ return 0;
+
+ /*
+ * Adjust the offset if this reloc applies to the percpu section.
+ */
+ if (sec->shdr.sh_info == per_cpu_shndx)
+ offset += per_cpu_load_addr;
+
+ switch (r_type) {
+ case R_X86_64_NONE:
+ case R_X86_64_PC32:
+ /*
+ * NONE can be ignored and PC relative relocations don't
+ * need to be adjusted.
+ */
+ break;
+
+ case R_X86_64_32:
+ case R_X86_64_32S:
+ case R_X86_64_64:
+ /*
+ * References to the percpu area don't need to be adjusted.
+ */
+ if (is_percpu_sym(sym, symname))
+ break;
+
+ if (shn_abs) {
+ /*
+ * Whitelisted absolute symbols do not require
+ * relocation.
+ */
+ if (is_reloc(S_ABS, symname))
+ break;
+
+ die("Invalid absolute %s relocation: %s\n",
+ rel_type(r_type), symname);
+ break;
+ }
+
+ /*
+ * Relocation offsets for 64 bit kernels are output
+ * as 32 bits and sign extended back to 64 bits when
+ * the relocations are processed.
+ * Make sure that the offset will fit.
+ */
+ if ((int32_t)offset != (int64_t)offset)
+ die("Relocation offset doesn't fit in 32 bits\n");
+
+ if (r_type == R_X86_64_64)
+ add_reloc(&relocs64, offset);
+ else
+ add_reloc(&relocs32, offset);
+ break;
+
+ default:
+ die("Unsupported relocation type: %s (%d)\n",
+ rel_type(r_type), r_type);
+ break;
+ }
+
+ return 0;
+}
+
+
+static int do_reloc32(struct section *sec, Elf_Rel *rel, Elf_Sym *sym,
+ const char *symname)
{
unsigned r_type = ELF32_R_TYPE(rel->r_info);
int shn_abs = (sym->st_shndx == SHN_ABS) && !is_reloc(S_REL, symname);
@@ -779,9 +1013,18 @@ static void emit_relocs(int as_text, int use_real_mode)
{
int i;
int (*write_reloc)(uint32_t, FILE *) = write32;
+ int (*do_reloc)(struct section *sec, Elf_Rel *rel, Elf_Sym *sym,
+ const char *symname);
+
+ if (ehdr.e_ident[EI_CLASS] == ELFCLASS64)
+ do_reloc = do_reloc64;
+ else if (!use_real_mode)
+ do_reloc = do_reloc32;
+ else
+ do_reloc = do_reloc_real;
/* Collect up the relocations */
- walk_relocs(use_real_mode ? do_reloc_real : do_reloc);
+ walk_relocs(do_reloc);
if (relocs16.count && !use_real_mode)
die("Segment relocations found but --realmode not specified\n");
@@ -789,6 +1032,7 @@ static void emit_relocs(int as_text, int use_real_mode)
/* Order the relocations for more efficient processing */
sort_relocs(&relocs16);
sort_relocs(&relocs32);
+ sort_relocs(&relocs64);
/* Print the relocations */
if (as_text) {
@@ -809,6 +1053,15 @@ static void emit_relocs(int as_text, int use_real_mode)
for (i = 0; i < relocs32.count; i++)
write_reloc(relocs32.offset[i], stdout);
} else {
+ if (ehdr.e_ident[EI_CLASS] == ELFCLASS64) {
+ /* Print a stop */
+ write_reloc(0, stdout);
+
+ /* Now print each relocation */
+ for (i = 0; i < relocs64.count; i++)
+ write_reloc(relocs64.offset[i], stdout);
+ }
+
/* Print a stop */
write_reloc(0, stdout);
@@ -876,6 +1129,8 @@ int main(int argc, char **argv)
read_strtabs(fp);
read_symtabs(fp);
read_relocs(fp);
+ if (ehdr.e_ident[EI_CLASS] == ELFCLASS64)
+ percpu_init();
if (show_absolute_syms) {
print_absolute_symbols();
goto out;
--
1.7.9.5
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